ASPTC Aspirated Thermocouple with Radiation ... - tp.cmdl.noaa.gov

Aspirated Thermocouple with Radiation Shield
Model ASPTC
Campbell Scientific's ASPTC uses a fine-wire thermocouple
mounted in an aspirated radiation shield to
provide highly accurate air temperature measurements.
One ASPTC can measure absolute air temperature, or
two ASPTCs can make delta temperature measurements.
Often, the ASPTC replaces, or is measured in addition
to, the TCBR thermocouples in a Bowen ratio system.
Thermocouple
The fine-wire thermocouple consists of a chromel wire
and a constantan wire joined at a measurement junction.
Temperature is determined by measuring the differences
in potential created at the junction of the two wires. A
reference temperature measurement (typically measured
at the datalogger wiring panel) is required. Options for
measuring the reference temperature include:
These Bowen ratio systems at a sorghum field near Lincoln,
Nebraska include ASPTCs attached to the upper and lower
Bowen ratio arms.
• CR10XTCR thermistor that connects to the CR10X wiring panel
• Thermistor built into the CR800, CR1000, CR3000, or CR5000 wiring panel
• PRT built into the wiring panel of the CR9050 or CR9051E input module for the CR9000X Measurement
and Control System
• PRT built into the wiring panel of the CR723T input card for the CR7 Measurement and Control System
Please note that our CR200-series and CR510 dataloggers are not compatible with thermocouples, and therefore
cannot be used to measure the ASPTC.
Aspirated Radiation Shield
The aspirated radiation shield consists of an elongated tube constructed from white UV stabilized polyethylene
that provides low thermal conductivity and heat retention. A fan draws air across the measurement junction,
which reduces solar loading on the thermocouple. The radiation shield also protects the thermocouple, increasing
the thermocouple's durability.
1.8" O.D.
↓
↑
mounting bracket
power cable
↕
2.3" O.D.
↑
↓
5.8"
thermocouple
signal cable
← 21" →

Mounting Options
The ASPTC can be mounted to a tripod or tower via the UT018 crossarm, a Bowen ratio arm, or a user-supplied
crossarm that has a square cross section (1.5" x 1.5"). When using a Bowen ratio arm, the ASPTC intake should be
mounted at the same height as the water vapor intake.
Power Considerations
The ASPTC is typically powered with a user-supplied deep cycle battery that is recharged with an SP20R or
SP65 solar panel; for high current drain systems two SP65 solar panels may be used to provide 130 W of power.
The datalogger's rechargeable battery can only be used if it is connected to ac power. For help on analyzing
your system’s power requirements, refer to our Power Supply product literature or application note.
Ordering Information
ASPTC-L-LP Aspirated Thermocouple with Radiation Shield and user-specified signal and power cable
lengths; enter the signal length (in feet) after the L and enter the power cable length (in feet)
after the -LP. In a standard configuration, lead lengths of 15' are recommended for both the
signal and power cables (ASPTC-L15-LP15).
UT018
BRA/UPR
BRA/LWR
Tower Mounting Bracket with 2' Crossarm
Upper Bowen Ratio Arm
Lower Bowen Ratio Arm
Specifications
Weight: 1.9 lbs (0.86 kg)
Shield
Material: UV stabilized polyethylene
Dimensions: 21” (53.3 cm ) length, 5.8” (14.7 cm) height, 2.3” (5.8 cm) large OD, 1.8” (4.6 cm) small OD
Fan
Air Velocity at Thermocouple: 5.5 m @ 12 Vdc
Life Expectancy : 60,000 hrs @ 25°C
Current Drain: 140 mA @ 25°C
Thermal Fuse: opens @ 640 mA
Operating Range: 6 to 14 Vdc
Radiation Error: